We’ve all experienced it. On a bright sunny morning, we see perfectly. But then it’s nighttime and our vision is significantly worse. “Why is my vision blurry at night” we wonder.
The same can be said for indoor spaces with poor lighting, or gloomy and cloudy autumn days. Humans don’t have the ability to easily adjust to darkness like nocturnal animals. But, healthy human eyes should still be able to function properly at night.
In this article, we’ll go over why vision can get blurry at night. We’ll explain in detail why this happens naturally, but also give you an overview of other possible causes for this problem.
Why Is My Vision Blurry at Night?
Less light means the image received by our retina is darker, has less contrast, and has less color. This (especially the lower contrast) means the brain has less information to read the image. But less light by itself does not lead to blur. Our eyes have a mechanism to adjust to different lighting conditions.
The dilation of the pupil is the main reason why blurry vision happens at night. The pupil is the central black circle located in the center of the eye. It is responsible for allowing light to enter the eye.
The pupil works the same way aperture works in photography. A large aperture will cause the background of a photo to become blurry. This is exactly what happens when you take a picture in portrait mode — it selects the largest possible aperture. The landscape mode does the exact opposite. It makes the aperture as small as possible, which results in the entire picture looking sharp and in focus.
When there’s less light available, because it’s cloudy outside or it’s beginning to get dark, our pupils automatically dilate without us even realizing. We only notice that our vision became less sharp.
Also, a dilated pupil reduces the ability to change focus between near and far objects. For example, when driving at night you may be “blinded” by street lights and headlights from oncoming cars. Just as it takes a while for your eyes to adjust when you enter a dark room, it also takes time for your eyes to adjust when a headlight appears. If you focus on the headlights, your pupils will constrict to block out the light.
Then, once the headlights have passed, your eyes will need time to readjust to the dark, making it difficult to see the road.
The lens of the human eye doesn’t have a perfect shape. Often the light rays that pass near the edge of a lens don’t focus at the same point as the light rays that pass through the central region of the lens. We call this spherical aberration.
Remember, at night the pupil is more dilated, allowing for more light to enter the eye through the area of the lens closer to the edge. Spherical aberration makes our vision at night more blurry.
Chromatic aberration is the failure of a lens to focus all colors to the same point. This is normal, however, different colors hit the eye in different ways. The image below is an exaggeration but illustrates the concept well:
Blue light — which is more common at night — is focused in front of the retina (the back of the eye). This is similar to the way light focuses in the eye of a person that has myopia (also known as nearsightedness). In order for vision to be perfectly clear, light has to focus exactly on top of the retina. This means that blue light rays are more likely to appear blurry to the human eye.
On the other hand, when light is predominantly red/orange (sunrise, sunset), our vision is better. This is because a large portion of the light will focus on top of the retina, or at least closer to it.
Throughout the 24 hours of a day, the spectrum of light outdoors is constantly changing due to weather conditions. Our vision changes with it.
Other Causes for Blurry Vision at Night
While pupil dilation, spherical aberration and chromatic aberration are somewhat normal to occur at night, especially if you already have myopia. Blurry vision in dark environments can have other causes:
- Uncorrected myopia. Meaning, you have a very small amount of myopia, and haven’t gone to an eye doctor to correct it.
- Deterioration of the eyes with age. This is part of the natural aging process.
- Lack of vitamin A. Are there enough carrots, sweet potatoes, mangoes, and spinach in your diet?
- Lack of zinc. Without it, vitamin A may not work as well as it should. Is there enough beef, beans, and nuts in your diet?
- Cataracts. The first symptom is often worse night vision.
- Diabetes. It makes you more likely to have night vision problems.
A simple exam with your local eye doctor can help you find an answer to the question “why is my vision blurry at night”.
In this article, we went over the reasons why vision gets blurry at night.
In most cases, night vision isn’t different from day vision. It’s just less light. And less light means less information for the eye. However, it can be indicative of a more serious problem.
Contact your eye doctor to confirm if you’re ok or if there’s reason to worry, especially if you have difficulty seeing while driving in the evening.
If you have any questions, leave them below in the comments! We’ll get back to you in less than 24 hours.
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